Disclosed herein are phase change ink compositions. More specifically, disclosed herein are curable phase change ink compositions. Further, the present disclosure generally relates to curable inks, particularly curable, phase change inks, and their use in methods for forming images, particularly their use in ink jet printing. One embodiment is directed to a phase change ink composition comprising (a) at least one curable monomer or prepolymer, (b) at least one gellant, (c) at least one hyperbranched polymer comprising at least one photoinitiating moiety, (d) a colorant (e) optionally, a reactive oligomer; and (f) optionally, at least one low molecular weight photoinitiator.
In general, phase change inks (sometimes referred to as “hot melt inks”) are in the solid phase at ambient temperature, but exist in the liquid phase at the elevated operating temperature of an ink jet printing device. At the jet operating temperature, droplets of liquid ink are ejected from the printing device and, when the ink droplets contact the surface of the recording substrate, either directly or via an intermediate heated transfer belt or drum, they quickly solidify to form a predetermined pattern of solidified ink drops. Phase change inks have also been used in other printing technologies, such as gravure printing, as disclosed in, for example, U.S. Pat. No. 5,496,879 and German Patent Publications DE 4205636AL and DE 4205713AL, the disclosures of each of which are totally incorporated herein by reference.
Phase change inks for color printing typically comprise a phase change ink carrier composition which is combined with a phase change ink compatible colorant. In a specific embodiment, a series of colored phase change inks can be formed by combining ink carrier compositions with compatible subtractive primary colorants. The subtractive primary colored phase change inks can comprise four component dyes, namely, cyan, magenta, yellow and black, although the inks are not limited to these four colors. These subtractive primary colored inks can be formed by using a single dye or a mixture of dyes. For example, magenta can be obtained by using a mixture of Solvent Red Dyes or a composite black can be obtained by mixing several dyes. U.S. Pat. No. 4,889,560, U.S. Pat. No. 4,889,761, and U.S. Pat. No. 5,372,852, the disclosures of each of which are totally incorporated herein by reference, teach that the subtractive primary colorants employed can comprise dyes from the classes of Color Index (C.I.) Solvent Dyes, Disperse Dyes, modified Acid and Direct Dyes, and Basic Dyes. The colorants can also include pigments, as disclosed in, for example, U.S. Pat. No. 5,221,335, the disclosure of which is totally incorporated herein by reference. U.S. Pat. No. 5,621,022, the disclosure of which is totally incorporated herein by reference, discloses the use of a specific class of polymeric dyes in phase change ink compositions.
Phase change inks have also been used for applications such as postal marking, industrial marking, and labeling.
Phase change inks are desirable for ink jet printers because they remain in a solid phase at room temperature during shipping, long term storage, and the like. In addition, the problems associated with nozzle clogging as a result of ink evaporation with liquid ink jet inks are largely eliminated, thereby improving the reliability of the ink jet printing. Further, in phase change ink jet printers wherein the ink droplets are applied directly onto the final recording substrate (for example, paper, transparency material, and the like), the droplets solidify immediately upon contact with the substrate, so that migration of ink along the printing medium is prevented and dot quality is improved.
Compositions suitable for use as phase change ink carrier compositions are known. Some representative examples of references disclosing such materials include U.S. Pat. No. 3,653,932, U.S. Pat. No. 4,390,369, U.S. Pat. No. 4,484,948, U.S. Pat. No. 4,684,956, U.S. Pat. No. 4,851,045, U.S. Pat. No. 4,889,560, U.S. Pat. No. 5,006,170, U.S. Pat. No. 5,151,120, U.S. Pat. No. 5,372,852, U.S. Pat. No. 5,496,879, European Patent Publication 0187352, European Patent Publication 0206286, German Patent Publication DE 4205636AL, German Patent Publication DE 4205713AL, and PCT Patent Application WO 94/04619, the disclosures of each of which are totally incorporated herein by reference. Suitable carrier materials can include paraffins, microcrystalline waxes, polyethylene waxes, ester waxes, fatty acids and other waxy materials, fatty amide containing materials, sulfonamide materials, resinous materials made from different natural sources (tall oil rosins and rosin esters, for example), and many synthetic resins, oligomers, polymers, and copolymers.
Ink jetting devices are known in the art, and thus extensive description of such devices is not required herein. As described in U.S. Pat. No. 6,547,380, incorporated herein by reference, ink jet printing systems generally are of two types: continuous stream and drop-on-demand. In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. The stream is perturbed, causing it to break up into droplets at a fixed distance from the orifice. At the break-up point, the droplets are charged in accordance with digital data signals and passed through an electrostatic field that adjusts the trajectory of each droplet in order to direct it to a gutter for recirculation or a specific location on a recording medium. In drop-on-demand systems, a droplet is expelled from an orifice directly to a position on a recording medium in accordance with digital data signals. A droplet is not formed or expelled unless it is to be placed on the recording medium.
There are at least three types of drop-on-demand ink jet systems. One type of drop-on-demand system is a piezoelectric device that has as its major components an ink filled channel or passageway having a nozzle on one end and a piezoelectric transducer near the other end to produce pressure pulses. Another type of drop-on-demand system is known as acoustic ink printing. As is known, an acoustic beam exerts a radiation pressure against objects upon which it impinges. Thus, when an acoustic beam impinges on a free surface (i.e., liquid/air interface) of a pool of liquid from beneath, the radiation pressure which it exerts against the surface of the pool may reach a sufficiently high level to release individual droplets of liquid from the pool, despite the restraining force of surface tension. Focusing the beam on or near the surface of the pool intensifies the radiation pressure it exerts for a given amount of input power. Still another type of drop-on-demand system is known as thermal ink jet, or bubble jet, and produces high velocity droplets. The major components of this type of drop-on-demand system are an ink filled channel having a nozzle on one end and a heat generating resistor near the nozzle. Printing signals representing digital information originate an electric current pulse in a resistive layer within each ink passageway near the orifice or nozzle, causing the ink vehicle (usually water) in the immediate vicinity to vaporize almost instantaneously and create a bubble. The ink at the orifice is forced out as a propelled droplet as the bubble expands.
In a typical design of a piezoelectric ink jet device utilizing phase change inks printing directly on a substrate or on an intermediate transfer member, such as the one described in U.S. Pat. No. 5,372,852, incorporated herein by reference, the image is applied by jetting appropriately colored inks during four to eighteen rotations (incremental movements) of a substrate (an image receiving member or intermediate transfer member) with respect to the ink jetting head, i.e., there is a small translation of the printhead with respect to the substrate in between each rotation. This approach simplifies the printhead design, and the small movements ensure good droplet registration. At the jet operating temperature, droplets of liquid ink are ejected from the printing device and, when the ink droplets contact the surface of the recording substrate, either directly or via an intermediate heated transfer belt or drum, they quickly solidify to form a predetermined pattern of solidified ink drops.
Hot melt inks typically used with ink jet printers have a wax based ink vehicle, e.g., a crystalline wax. Such solid ink jet inks provide vivid color images. In typical systems, these crystalline wax inks partially cool on an intermediate transfer member and are then pressed into the image receiving medium such as paper. Transfuse spreads the image droplet, providing a richer color and lower pile height. The low flow of the solid ink also prevents showthrough on the paper.
In these systems, the crystalline wax inks are jetted onto a transfer member, for example, an aluminum drum, at temperatures of approximately 130-140° C. The wax based inks are heated to such high temperatures to decrease their viscosity for efficient and proper jetting onto the transfer member. The transfer member is at approximately 60° C., so that the wax will cool sufficiently to solidify or crystallize. As the transfer member rolls over the recording medium, e.g., paper, the image comprised of wax based ink is pressed into the paper.
Radiation curable inks generally comprise at least one curable monomer, a colorant, and a radiation activated initiator, specifically a photoinitiator, that initiates polymerization of curable components of the ink, specifically of the curable monomer. Photoinitiators are typically low molecular weight compounds, low molecular weight compounds generally being compounds having a molecular weight of from about 100 to about 1000 or from about 100 to less than about 800. The low molecular weight photoinitiator compounds are not substantially incorporated into the polymer matrix formed after polymerization of radiation curable ink compositions. As a result, residual photoinitiators and bi-products thereof can diffuse out of cured products and can be extracted. When used in certain applications, for example food packaging, and direct to paper printing, it is desirable to reduce the amount of or eliminate altogether extractable species present, for example to meet environmental, health and safety requirements.
U.S. Patent Publication 20060014852 (Loccufler et al.) the disclosure of which is totally incorporated herein by reference, discloses a radiation curable composition comprising a novel photoreactive polymer comprising a dendritic polymer core with at least one initiating functional group and at least one co-initiating functional group. Suitable radiation curable compositions are varnishes, lacquers, printing inks and radiation curable ink-jet inks. The dendritic polymeric core is preferably a hyperbranched polymer.
While known compositions and processes are suitable for their intended purposes, a need remains for improved photoinitiators. In addition, a need remains for improved phase change inks. Further, a need remains for photoinitiators that are soluble in, miscible in, or otherwise compatible with phase change ink vehicles. Additionally, a need remains for photoinitiators that lead to reduced odor when used in curable phase change inks prior to curing. There is also a need for photoinitiators that lead to reduced odor when used in curable phase change inks subsequent to curing. In addition, there is a need for photoinitiators that lead to reduced surface yellowing in images when used in curable phase change inks. Further, there is a need for photoinitiators that exhibit reduced migration through cured images when used in curable phase change inks. Additionally, there is a need for photoinitiators having improved affinity for phase change inks exhibiting a gel phase during the printing process. A need also remains for a photoinitiator having reduced volatility in itself and also having reduced volatility of its fragments. In addition, a need remains for photoinitiators that in themselves exhibit gellant characteristics. Further, a need remains for photoinitiators that have improved affinity for the ordered microstructure of the gel phase, as opposed to being excluded from that order. Additionally, a need remains for photoinitiators that are themselves curable. There further remains a need for phase change inks with reduced or eliminated amounts of post fusing extractable species. There further remains a need for phase change inks that can be tuned with respect to ink rheology independently from the selection of curable monomer, oligomer or prepolymer.
The appropriate components and process aspects of the each of the foregoing may be selected for the present disclosure in embodiments thereof.